In recent years, power semiconductors have been widely used in automobile electronics, power management and automation technology. Those power semiconductors are generally combined to form modules which are tailored to fit customer-specific requirements.
In such power semiconductor modules, individual electronic components are generally mounted on a substrate. The substrate is usually produced in the form of a sandwich, with a ceramic plate sandwiched between two outer metal plates. Those metal plates are generally made of copper, since copper has very good properties in terms of electrical conductivity and thermal conductivity. The substrate having the copper/ceramic/copper sandwich structure is referred to as a direct bonded copper (DBC) substrate. The DBC substrate has two layers of copper bonded onto a ceramic base, carrying high currents and providing high voltage isolation.
High power IGBT module is commonly used in the industry. The module is expected to provide ultra high power up to Mega Watt (MW), long service life up to 15 years, and operating temperature up to 200° C. Ceramic based direct bonded copper is frequently used as a dielectric carrier, and the corresponding sealing comprises silicone and plastic housing. FIG. 1 is a schematic diagram showing a conventional IGBT module according to a prior art. Comparing with microelectronics, power electronics have to meet a series of harsh requirements such as long power cycling, vibration test with high impacts, and long lifetime. Thus, there are lots of inventions relating to this area.
U.S. Pat. No. 6,715,203 provides a substrate for power semiconductor modules with a through-plating of solder, including two metal plates and a ceramic plate which is seated as a layer between the metal plates and has a through hole formed therein. The substrate is plated through by making a through hole in one of the metal plates in alignment with the through hole in the ceramic plate and applying a paste solder to one side of the substrate. The substrate is then subjected to a furnace step, so that the paste solder flows into the through holes and the solder makes a permanent contact between the two metal plates. Nevertheless, the through hole with solder provides electric connection of both surfaces of the ceramic layer.
U.S. Pat. No. 6,703,707 provides a semiconductor device including two semiconductor chips that are interposed between a pair of radiation members, and thermally and electrically connected to the radiation members. One of the radiation members has two protruding portions and front ends of the protruding portions are connected to principal electrodes of the semiconductor chips. The radiation members are made of a metallic material containing Cu or Al as a main component. The semiconductor chips and the radiation members are sealed with resin with externally exposed radiation surfaces. However, the chips interposed between the two metal blocks provide no voltage isolation.
U.S. Pat. No. 5,465,898 discloses a process provided where a ceramic metal substrate is produced by attaching metal foils on either side a ceramic layer to form metal layers and for producing a through connection by placing metal in an opening to form a bridge so that the metal layers are electrically connected together by direct bonding, and a metal body is inserted into the opening to almost fill it, while a surface of the metal body is provided with a layer with chemical compound of metal and reactive gas. However, the metal bridge makes electric connection of both surfaces of ceramic layer.
Nevertheless, insufficient module protection may lead to fail in stringent reliability tests. FIG. 2 is a photo showing a directed bonded copper substrate failed after about 100 temperature cycles according to a prior art. The copper layer is peeled off from the ceramic layer, and such failure is come from the coefficient of thermal expansion (CTE) mismatch between the core ceramic and the bonded copper.
Consequently, there is an unmet need for a power electronics module that provides high reliability and long lifetime.